Method and device for cooling circulating air

ABSTRACT

Circulating air is cooled by heat exchange with adiabatically cooled process air. To this end, a first heat exchanging device is fed with circulating air and the process air. The heat exchanging device contains a humidifying device used to spray water into the process air. In this way, the process air is adiabatically cooled and the corresponding cooling is carried out by heat exchange with the circulating air. Before entering the first heat exchanging device and before leaving same, the process air is guided through a second heat exchanging device in which the cooled process air first extracts heat from the uncooled process air. This increases the cooling performance of the device.

The invention relates to a method and an apparatus for coolingcirculating air by means of heat exchange with adiabatically cooledprocess air.

The invention is the field of so-called indirect adiabatic cooling sincethe water necessary for the adiabatic cooling is not introduced into thecirculating air but into the process air, which is preferablyatmospheric air. The adiabatically cooled process air constitutes anenthalpy sink which comes into heat exchange with the circulating airand reduces its temperature.

The cooling capacity of such systems depends on the starting temperatureand humidity of the process air. If this temperature is e.g. relativelyhigh, the cooling capacity is inadequate to effectively cool thecirculating air. One was therefore previously obliged to use anadditional cooling installation of compression or absorption type.

Such cooling installations increase the technical complexity of theapparatus. They consume high grade energy in the form of electriccurrent or fossil fuels and also operate with environmentally harmfulrefrigerants. Legal regulations are increasingly necessary whichregulate the consumption of high grade energy and the use ofenvironmentally harmful substances.

It is the object of the invention to increase the efficiency of indirectadiabatic cooling of circulating air with simple means.

In order to solve this object, the method referred to above ischaracterised in accordance with the invention in that after its heatexchange with the circulating air, the cooled process air absorbs heatfrom the uncooled process air.

After its heat exchange with the circulating air, the cooled process airhas a temperature, which is below the temperature of the uncooledprocess air. It can thus absorb heat from the uncooled process air sothat its temperature decreases. The adiabatic cooling thus acts onprocess air, whose temperature has already been reduced. This is to thebenefit of the cooling of the circulating air with the result thatadditional cooling installations of compression or absorption type canbe omitted, in applications in which the sensible cooling of thecirculating air is sufficient. The technical apparatus cost necessaryfor this purpose is low. In addition to the investment costs, theoperating costs also decrease since less energy and less water areconsumed.

It is also to be emphasised that no approval process is necessary foroperation of the cooling installation. Maintenance is simplified becauseno refrigeration specialist need be consulted. All damage to theenvironment resulting from the use of refrigerants is also eliminated.

The adiabatic cooling of the process air can occur before the processair comes into heat exchange with the circulating air. One can thenrefer to a two-stage evaporation process. A single stage evaporationprocess can be more advantageous, in which the adiabatic cooling of theprocess air is effected in heat exchange with the circulating air. Incontrast to the two stage evaporation process, the heat exchangesurfaces are wetted with the injected water.

Depending on the operational state, the water temperature can varyduring the single stage adiabatic cooling. Surprisingly, it has beenfound that important effects on the conduct of the method are produced.If the water temperature decreases, it is advantageous to conduct thecirculating air and the process air in co-current in the heat exchangeprocess. In other cases, counter current is more favourable. It is thusproposed in embodiments of the invention that the circulating air andthe process air be conducted either in co-current, counter current orcross-current or in cross-co-current or cross-counter current during theheat exchange process.

The cooling performance is preferably controllable by variation of thecirculating air/process air mass flow ratio and/or by variation of theamount of water introduced into the process air.

The cooled process air is preferably exhausted after it has absorbedheat from the uncooled process air.

The apparatus for solving the object posed has a first heat exchangerdevice, which may be fed with the circulating air and with process air,and a moistening device for introducing water into the process air andis characterised in accordance with the invention by a second heatexchanger device for heat exchange between the uncooled process air,before its entry into the first heat exchanger device, and the cooledprocess air, after its discharge from the heat exchanger device. Theprocess air thus flows firstly through the second heat exchanger deviceand then through the first heat exchanger device, whereafter it isdiverted through the second heat exchanger device. The cooled processair absorbs heat from the uncooled process air in the second heatexchanger device and thus reduces its temperature.

The second heat exchanger device may advantageously be bypassed, atleast on the inlet side of the uncooled process air, by means of abypass in the event that the temperature of the uncooled process airmakes pre-cooling it in the second heat exchanger device unnecessary.Having regard to this aspect, the moistening device may preferably alsobe switched off. Finally, a preferred possibility resides in operatingwith so-called free cooling, in which the atmospheric air is useddirectly for cooling the space.

The moistening device can be in the form of a scrubber, a contactmoistener, a high pressure moistener or the like. It can be locatedbetween the first and second heat exchanger devices. This type ofarrangement can, as mentioned, be referred to as two-stage evaporation.Single stage evaporation, in which the moistening device is integratedin the first heat exchanger device, is, under certain circumstances,more advantageous. The water is thus injected directly into the firstheat exchanger device and wets its heat exchange surfaces.

The first heat exchanger device is preferably operable in countercurrent, co-current or cross-current, depending on whether thetemperature of the water increases or decreases in the adiabaticcooling.

It is proposed in an important embodiment of the invention that thefirst heat exchanger device has at least two cross-current heatexchangers, these preferably being operable in cross-counter current orcross-co-current.

The process air is advantageously exhausted by a blower, which isarranged in the pathway of the process air downstream of the second heatexchanger device. The blower thus sucks the process air through theapparatus. The arrangement is such that the heating of the process airnecessarily produced by the blower does not impair the coolingperformance.

The invention will be explained in more detail below with reference to apreferred exemplary embodiment in conjunction with the attached drawing,in which:

FIG. 1 is a schematic view of an apparatus in accordance with theinvention;

FIG. 2 shows the changes in state of the circulating air and of theprocess air in an h, x-diagram.

As shown in FIG. 1, a first heat exchanger device 1 is provided, whichincludes two cross current heat exchangers 2 and 3. The first heatexchanger device 1 has circulating air applied to it and this firstlyflows through the cross-flow heat exchanger 2 and then through thecross-flow heat exchanger 3. A blower 5 is responsible for the movementof the circulating air.

The first heat exchanger device 1 also has process air 6 applied to it,which is atmospheric air in the present case. The process air also flowsfirstly through the cross-flow heat exchanger 2 and then through thecross-flow heat exchanger 3. The first heat exchanger device 1 thusoperates in cross-co-current, which is advantageous because theoperational state of the apparatus results in cooling of the waterinjected into the first heat exchanger device 1.

For this purpose, the first heat exchanger device 1 is provided with amoistening device 7, which sprays the water into the process air 6 andthus effects adiabatic cooling thereof. The water accumulates in a sump8 and is applied to the moistening device 7 by a pump 9. The sump 8 isprovided with a water supply 10 and a water drain 11.

Before entry into the first heat exchanger device 1 and after dischargefrom it, the process air 6 flows through a second heat exchanger device12 under the action of a blower 13, which is arranged downstream of thesecond heat exchanger device 12, with respect to the cooled process air.The heat generated by the blower 13 can not impair the coolingperformance. Since the temperature of the cooled process air 6 is lower,after discharge from the first heat exchanger device 1, than thetemperature of the process air 6 before entry into the second heatexchanger device 12, heat exchange can occur in the latter between thetwo flows of the process air with the result that the process air 6 issubjected to the adiabatic cooling with a reduced temperature. Theresult is a corresponding increase in the cooling performance.

Figure is a h,x-diagram showing an example of one-stage adiabaticcooling, as may be performed with the apparatus of FIG. 1, a line aindicating the temperature reduction of the circulating air 4 in thefirst heat exchanger device 1. A line b shows the temperature reductionexperienced by the process air 6 in the second heat exchanger device 12.A line c indicates the temperature reduction of the process air 6 as aresult of the adiabatic cooling in the first heat exchanger device 1 anda line d indicates the temperature increase of the process air 6 in thesecond heat exchanger device 12.

Modifications are of course possible within the scope of the invention.Thus the conveying direction of the blower 5 can be reversed. The firstheat exchanger device 1 then operates in cross-counter flow mode. Thismode of operation will be selected if the water temperature does notdecrease between the process air inlet and outlet. There is also thepossibility of decoupling the moistening device from the first heatexchanger device and permitting it to operate between the two heatexchanger devices. The integration of the moistening device into thefirst heat exchanger device is, however, particularly advantageous. Thefirst heat exchanger device can be of single stage construction but canhave a multi-stage construction, as also can the second heat exchangerdevice. There is also the possibility of bypassing the second heatexchanger device with a bypass, whereby the lines b and d in the diagramof FIG. 2 disappear. If, as is also possible, the moistening device 7 isswitched off, line c also disappears. The cooling effect then resultsonly from the temperature difference the circulating air and the processair. Finally, the first heat exchanger device can also be decoupled. Theprocess air is then blown directly into the space to be cooled.

1. A method of cooling circulating air by means of heat exchange withadiabatically cooled process air, characterised in that after its heatexchange with the circulating air, the cooled process air absorbs heatfrom the uncooled process air.
 2. A method as claimed in claim 1,characterised in that the adiabatic cooling of the process air iseffected in a single stage in the heat exchange with the circulatingair.
 3. A method as claimed in claim 1, characterised in that thecirculating air and the process air are conducted in co-current in theheat exchange process.
 4. A method as claimed in claim 1, characterisedin the circulating air and the process air are conducted incounter-current in the heat exchange process.
 5. A method as claimed inclaim 1, characterised in that the circulating air and the process airare conducted in cross-current in the heat exchange process.
 6. A methodas claimed in claim 1, characterised in that the circulating air and theprocess air are conducted in cross-co-current through two cross-flowheat exchangers (2, 3) in the heat exchange process.
 7. A method asclaimed in claim 1, characterised in that the circulating air and theprocess air are conducted in cross-counter current through cross-flowheat exchangers (2, 3) in the heat exchange process.
 8. A method asclaimed in claim 1, characterised in that the cooling performance iscontrolled by variation of the circulating air/process air mass flowratio.
 9. A method as claimed in claim 1, characterised in that thecooling performance is controlled by variation of the amount of waterintroduced into the process air.
 10. A method as claimed in claim 1,characterised in that the cooled process air is exhausted after it hasabsorbed heat from the uncooled process air.
 11. Apparatus for coolingcirculating air (4) including a first heat exchanger device (1), whichmay be fed with the circulating air (4) and with process air (6), and amoistening device (7) for introducing water into the process air (6),characterised by a second heat exchanger device (12) for heat exchangebetween the uncooled process air (6) before its entry into the firstheat exchanger device (1) and the cooled process air (6) after itsdischarge from the first heat exchanger device (1).
 12. Apparatus asclaimed in claim 11, characterised in that the second heat exchangerdevice (12) may be bypassed, at least on the inlet side of the uncooledprocess air (6), via a bypass.
 13. Apparatus as claimed in claim 11,characterised in that the moistening device (7) may be switched off. 14.Apparatus as claimed in claim 11, characterised in that a moisteningdevice (7) is integrated in the first heat exchanger device (1). 15.Apparatus as claimed in claim 11, characterised in that the first heatexchanger device (1) is operable in co-current.
 16. Apparatus as claimedin claim 11, characterised in that the first heat exchanger device (1)is operable in counter-current.
 17. Apparatus as claimed in claim 11,characterised in that the first heat exchanger device (1) is operable incross-current.
 18. Apparatus as claimed in claim 11, characterised inthat the first heat exchanger device (1) includes at least twocross-current heat exchangers (2, 3).
 19. Apparatus as claimed in claim18, characterised in that the first heat exchanger device (1) isoperable in cross-co-current.
 20. Apparatus as claimed in claim 18,characterised in that the first heat exchanger device (1) is operable incross-counter current.
 21. Apparatus as claimed in claim 11,characterised by a blower (13) for exhausting the process air (6)arranged in the pathway of the cooled process air (6) downstream of thesecond heat exchanger device (12).